External Public-Key Authentication API (#72) * Implemented dynamic loading of an external plug-in shared library to delegate public key authentication * Moved conditional compilation of the plugin infrastructure into the configure.ac script to be able to add -ldl to dropbear build only when the flag is enabled * Added tags file to the ignore list * Updated API to have the constructor to return function pointers in the pliugin instance. Added support for passing user name to the checkpubkey function. Added options to the session returned by the plugin and have dropbear to parse and process them * Added -rdynamic to the linker flags when EPKA is enabled * Changed the API to pass a previously created session to the checkPubKey function (created during preauth) * Added documentation to the API * Added parameter addrstring to plugin creation function * Modified the API to retrieve the auth options. Instead of having them as field of the EPKASession struct, they are stored internally (plugin-dependent) in the plugin/session and retrieved through a pointer to a function (in the session) * Changed option string to be a simple char * instead of unsigned char *

/* LibTomCrypt, modular cryptographic library -- Tom St Denis
 *
 * LibTomCrypt is a library that provides various cryptographic
 * algorithms in a highly modular and flexible manner.
 *
 * The library is free for all purposes without any express
 * guarantee it works.
 */

#include "tomcrypt.h"

#ifdef LTC_MDH

/**
  Binary export a DH key to a buffer
  @param out    [out] The destination for the key
  @param outlen [in/out] The max size and resulting size of the DH key
  @param type   Which type of key (PK_PRIVATE or PK_PUBLIC)
  @param key    The key you wish to export
  @return CRYPT_OK if successful
*/
int dh_export_key(void *out, unsigned long *outlen, int type, dh_key *key)
{
   unsigned long len;
   void *k;

   LTC_ARGCHK(out    != NULL);
   LTC_ARGCHK(outlen != NULL);
   LTC_ARGCHK(key    != NULL);

   k = (type == PK_PRIVATE) ? key->x : key->y;
   len = mp_unsigned_bin_size(k);

   if (*outlen < len) {
      *outlen = len;
      return CRYPT_BUFFER_OVERFLOW;
   }
   *outlen = len;

   return mp_to_unsigned_bin(k, out);
}

#endif /* LTC_MDH */

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